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PDF MIC2871 Data sheet ( Hoja de datos )
| Número de pieza | MIC2871 | |
| Descripción | 1.2A High-Brightness LED Flash Driver | |
| Fabricantes | Micrel Semiconductor | |
| Logotipo |  |
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MIC2871
1.2A High-Brightness LED Flash Driver with
Single-Wire Serial Interface
General Description
The MIC2871 is a high-current, high-efficiency flash LED
driver. The LED driver current is generated by an
integrated inductive boost converter with a 2MHz switching
frequency which allows the use of very small inductor and
output capacitor. These features make the MIC2871 an
ideal solution for high-resolution camera phone LED flash
light driver applications.
The MIC2871 operates in either flash or torch modes that
can be controlled through the single-wire serial interface
and/or external control pins. Default flash and torch
brightness can be adjusted via an external resistor. A
robust single-wire serial interface allows simple control by
the host processor to support typical camera functions
such as auto-focus, white balance, and image capture
(flash mode).
The MIC2871 is available in a 14-pin 3mm × 2mm LDFN
package with a junction temperature range of −40°C to
+125°C.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Features
• Up to 1.2A flash LED driving current
• Highly-efficient, synchronous boost driver (up to 94%)
• ±5% LED current accuracy
• Control through single-wire serial interface or external
control pins
• Input voltage range: 2.7V to 5.5V
• True load disconnect
• Configurable safety time-out protection
• Output overvoltage protection (OVP)
• LED short detection and protection.
• 1µA shutdown current
• Available in 14-pin 3mm × 2mm LDFN package
Applications
• Camera phones/mobile handsets
• Cell phones/smartphones
• LED light for image capture/auto focus/white balance
• Handset video light (torch light)
• Digital cameras
• Portable applications
Typical Application
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
May 29, 2013
052913-1.0 (while in progress)
Revision 1.0 (final document)
1 page  
Micrel, Inc.
Typical Characteristics
Shutdown Current
vs. Temperature
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
WLED Power Efficiency
vs. Input Voltage
100
90
80 ILED = 1.0A
ILED = 1.2A
ILED = 640mA
70
ILED = 400mA
60
L = 1µH
COUT = 4.7µF
ILED = 250mA
ILED = 100mA
50
2.6
3.0 3.4 3.8 4.2
INPUT VOLTAGE (V)
4.6
5.0
Flash Mode ILED(MAX)
vs. FRSET Resistor
1200
1000
800
600
400
200
L = 1 µH
COUT = 4.7µF
0
0 10 20 30 40 50
FRSET RESISTOR (kΩ)
60
Standby Current
vs. Temperature
245
240
235
230
225
220
-40
-20 0 20 40 60 80
TEMPERATURE (°C)
100 120
Torch Mode LED Current
vs. Temperature
270
265
260
255
250
245
240
235
230
-40 -20
L = 1µH
COUT = 4.7µF
ILED = 250mA
RFRSET = 20kΩ
0 20 40 60 80 100 120
TEMPERATURE (°C)
Torch Mode ILED(MAX)
vs. FRSET Resistor
300
250
200
150
100
50 L = 1 µH
COUT = 4.7µF
0
0 10 20 30 40 50
FRSET RESISTOR (kΩ)
60
MIC2871
Boost Switching Frequency
vs. Input Voltage
2.20
2.15
-40°C
2.10 25°C
2.05
2.00
1.95
1.90
1.85
L = 1 µH
COUT = 1µF
ILED = 1A
75°C
125°C
1.80
2.5 3.0 3.5 4.0
INPUT VOLTAGE (V)
4.5
Flash Mode LED Current
vs. Temperature
1.20
1.15
1.10
1.05
1.00
0.95
0.90
0.85
0.80
-40 -20
L = 1µH
COUT = 4.7µF
ILED = 1A
RFRSET = 20kΩ
0 20 40 60 80 100 120
TEMPERATURE (°C)
Flash Mode ILED(MAX)
Accuracy vs. Input Voltage
3.5
3.0 RFRSET = 17kΩ
2.5
2.0
1.5
1.0
0.5
0.0 RFRSET = 30kΩ
-0.5 RFRSET = 39kΩ
RFRSET = 51kΩ
-1.0
RFRSET = 20kΩ
-1.5 RFRSET = 62kΩ
3.5 3.7
3.9
4.1
INPUT VOLTAGE (V)
4.3
May 29, 2013
5 052913-1.0 (while in progress)
Revision 1.0 (final document)
5 Page 
Micrel, Inc.
Application Information
The MIC2871 can drive a high-current flash WLED in
either flash mode or torch mode.
Boost Converter
The internal boost converter is turned on/off automatically
when the LED driver is activated/de-activated without any
exception.
The boost converter is an internally-compensated
current-mode PWM boost converter running at 2MHz. It
is for stepping up the supply voltage to a high enough
value at the OUT pin to drive the LED current. If the
supply voltage is high enough, the synchronous switch of
the converter is then fully turned on. In this case, all the
excessive voltage is dropped over the linear LED driver.
Flash Mode
The maximum current level in the flash mode is 1.2A.
This current level can be adjusted through an external
resistor connecting to the FRSET pin according to
Equation 1:
ILED(MAX)
=
20500
R FRSET
Eq. 1
Alternatively, the default value of 1A is used when the
FRSET pin is grounded.
The flash mode current can be initiated at this preset
FRSET brightness level by asserting FEN1 or FEN2 pin
HIGH, or by setting the flash control register (address 1),
for the desired flash duration, subjected to the safety
timeout setting. The flash mode current is terminated
when the FEN1 and FEN2 pins are brought LOW and the
flash register is cleared.
Flash mode current can be adjusted to a fraction of the
maximum flash mode current level by selecting the
desired percentage in the flash control register through
the single-wire serial interface. The flash current is the
product of the maximum flash current setting and the
percentage selected in the flash register.
Torch Mode
By default, the maximum torch mode level is one-fourth
(1/4) of the maximum flash mode current. The torch
mode operation is activated by setting the torch control
register (address 2) for the desired duration. The torch
mode current is terminated when the torch register is
cleared or when the configurable safety timer expires.
MIC2871
Like the flash mode current, the torch mode current can
be tuned to a fraction of the maximum torch mode level
by selecting the desired torch current level percentage in
the torch control register (address 2) through the single-
wire serial interface.
The torch current is the product of the maximum Torch
current setting and the percentage selected in the torch
register.
Configurable Safety Timer
The flash safety timeout feature automatically shuts down
the LED current after the safety timer duration is expired
if the programmed LED current exceeds a certain current
threshold. Both the current threshold and the timer
duration are programmable via the safety timer registers
(addresses 3 and 5).
Low-Battery Voltage Detection (LBVD)
When the VIN voltage drops below the LBVD threshold
(default = 3.6V) in flash or torch mode, the LED current
driver is disabled. The LED driver can be resumed by
toggling the corresponding input control signal. The
LBVD threshold is adjustable thru the LBVD control
register (address 4).
Overvoltage Protection
When the output voltage rises above the OVP threshold,
MIC2871 is latched off automatically to avoid permanent
damage to the IC. To clear the latched off condition,
either power cycle the MIC2871 or assert the DC pin
LOW.
Short-Circuit Detection
Each time before enabling the LED driver, the MIC2871
performs the short circuit test by driving the flash LED
with a small (2mA typical) current for 200µs. If (VOUT –
VLED) < 1.7V at the end of the short-circuit test, the LED is
considered to be shorted and MIC2871 will ignore the
flash and/or torch mode command. Note that the short-
circuit test is carried out every time prior to flash and
torch mode but the result is not latched.
Thermal Shutdown
When the internal die temperature of MIC2871 reaches
155°C, the LED driver is disabled until the die
temperature falls below 140°C.
May 29, 2013
11 052913-1.0 (while in progress)
Revision 1.0 (final document)
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet MIC2871.PDF ] | |
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